Semiconductor

Semiconductors conduct electricity less readily than metals but more readily than good insulators. Their behavior is not fixed: temperature, light and small quantities of impurity atoms can change how easily electric charge moves through them. In a crystal, electrons and the positively charged vacancies they leave behind, called holes, can both carry current. These controllable properties make semiconductors useful for devices that sense, direct or switch electrical signals.

Silicon is the dominant material in integrated-circuit manufacturing; germanium and compound materials such as gallium arsenide are also used for particular applications. Manufacturers can alter a material's electrical behavior by adding carefully controlled trace amounts of other elements, a process called doping. In a simplified description, n-type material has electrons as its majority charge carriers, while p-type material has holes as its majority carriers. Joining these regions creates a p–n junction, a basic structure used in semiconductor devices.

A p–n junction can conduct current more readily in one direction than the other, making it useful as a diode. Transistors use semiconductor structures to control current or voltage, allowing them to amplify signals or act as switches. Large numbers of transistors and other components can be fabricated together on a small piece of semiconductor to form an integrated circuit, or chip. Semiconductors also convert between light and electricity in devices such as photodetectors, light emitters and solar cells.

Before transistors, semiconductor components such as crystal rectifiers were used to detect or rectify electrical signals. The first point-contact transistor was demonstrated at Bell Telephone Laboratories in 1947 by John Bardeen and Walter Brattain. Integrated-circuit development followed in 1958 and 1959, when Jack Kilby and Robert Noyce developed ways to make multiple circuit components together on semiconductor material. These advances made it practical to build increasingly compact and complex electronic systems.

Turning a semiconductor crystal into a chip involves tightly controlled materials and manufacturing processes that define and connect many microscopic device regions. The resulting chips are used in computers, communications equipment, vehicles, medical devices, data centers and many other systems. Silicon remains the main material for most integrated circuits, while other semiconductors are selected when their electrical or optical properties better suit a task. Semiconductor fabrication and supply chains are specialized and international, making the field important to research, industry and public policy.